The field to which the present invention relates is that generally known as electrical discharge machining, sometimes hereinafter referred to as EDM, in which material is removed from an electrically conductive workpiece by the action of electrical gap discharges occurring between a tool electrode and a workpiece. A dielectric coolant fluid is circulated and recirculated through the gap, usually under pressure, throughout the machining operation. An electrode or a workpiece servo feed system is used to provide a relative movement and thus maintain an optimum gap spacing between the electrode and the workpiece as the workpiece material is being removed. A number of electrical discharge machining servo feed systems are known in the prior art that are of the basic analog type.
Examples of these are U.S. Pat. No. 4,152,569 issued on May 1, 1979 to Oliver A. Bell, Jr. et al for "Servo Feed Circuit for Electrical Discharge Machining Apparatus". This patent shows and describes a feedback circuit for control of servo velocity on up feed and down feed.
U.S. Pat. No. 3,793,502 issued on Feb. 19, 1974 to Oliver A. Bell, Jr. for "Servo Feed Circuit for Electrical Discharge Machining Apparatus". This servo feed system includes a plurality of reference voltage potentiometers and operational amplifiers with a specialized summing arrangement for different polarity operations.
U.S. Pat. No. 3,727,024 issued on Apr. 10, 1973 to Oliver A. Bell, Jr. for "Electrical Discharge Machining Servo Control Circuit". This patent discloses and describes a particular "keyed" servo feed circuit including a field effect transistor.
As electrical discharge machining power supplies and machine tools became more sophisticated, it became a common design goal to take away many of the adjustments and to lessen the degree of judgment required of an operator. It is desireable to make the operation automatic wherever possible so that the equipment may run on an around-the-clock basis with limited operator attention. In line with this course of development, systems have been devised which included computer control or control by stored input data that promise to a degree to provide this objective. One such system showing servo feed mechanism is described and shown in U.S. Pat. No. 4,071,729 issued on Jan. 31, 1978 to Oliver A. Bell, Jr. for "Adaptive Control System and Method for Electrical Discharging Machining".